The present invention relates to a method for epitaxially forming a layer of monocrystalline silicon. More particularly, it relates to a process for fabricating monocrystalline silicon on an apertured mask layer which is disposed on a monocrystalline substrate.
In the field of semiconductor device processing epitaxially deposited silicon is commonly used in a variety of applications. Basically, this deposition involves the precipitation of silicon from a source gas onto a crystal lattice, such that the deposited silicon forms a structure which continues the crystal lattice. Conventionally used silicon-source gases include silane (SiH.sub.4), silicon tetrachloride (SiCl.sub.4), trichlorosilane (SiHCl.sub.3), and dichlorosilane (SiH.sub.2 Cl.sub.2), and the details of typical processing are described in ADVANCES IN DICHLOROSILANE EPITAXIAL TECHNOLOGY, D. J. DeLong, Solid State Technology, October 1972, pp. 29-34, 41, and in U.S. Pat. No. 3,945,864, METHOD OF GROWING THICK EPITAXIAL LAYERS OF SILICON, N. Goldsmith et al, issued Mar. 23, 1976. The quality and rate of silicon deposition is a strong function of such parameters as deposition temperature and specific gas composition, as elaborated upon in U.S. Pat. No. 3,239,372, METHOD OF PRODUCING SINGLE CRYSTALLINE SILICON, E. Sirtl, issued Mar. 8, 1966, as well as in the previously cited references.
Epitaxial films of silicon have been selectively grown within the apertures of a silicon dioxide (SiO.sub.2) mask on the surface of a single-crystalline silicon substrate. An example of such a process is described in SELECTIVE EPITAXIAL DEPOSITION OF SILICON, B. D. Joyce et al, Nature, Vol. 195, pp. 485, 6, Aug. 4, 1962. Selective epitaxial deposition has also been used to form a grid of monocrystalline silicon islands wherein the grid is specified by a particular center-to-center spacing of an array of apertures in a silicon dioxide layer, and wherein each silicon island overgrows the silicon dioxide surrounding each aperture a specific distance. An example of such an overgrown structure and its manufacturing method is described in THE "EPICON" ARRAY: A NEW SEMICONDUCTOR ARRAY-TYPE CAMERA TUBE STRUCTURE, W. E. Engeler et al, Applied Physics Letters, Vol. 16, No. 5, Mar. 1, 1970; THE EPICON CAMERA TUBE: AN EPITAXIAL DIODE ARRAY VIDICON, S. M. Blumenfeld et al, IEEE Trans., Vol. ED18, No. 11, November 1971; and in U.S. Pat. No. 3,746,908, SOLID STATE LIGHT SENSITIVE STORAGE ARRAY, W. E. Engeler, issued July 17, 1973.
As suggested by the cited references, the process of epitaxially depositing monocrystalline silicon is well established in the semiconductor industry. For example, the effect of reaction temperature, deposition gas composition, and gas flow rate on both the quality and deposition rate is well characterized. It is well-known that while monocrystalline silicon will nucleate on a monocrystalline substrate, a monocrystalline layer will not be nucleated on a polycrystalline or amorphous surface. Typically, when a non-single-crystalline surface, such as the surface of a silicon dioxide layer, is subjected to an epitaxial deposition environment, a non-single-crystalline silicon film will be deposited.
Heretofore, the formation of monocrystalline silicon on silicon dioxide was achieved by creating a grid of monocrystalline silicon islands as disclosed by Engeler and Blumenfeld. This process relies on the migration of silicon atoms across the oxide surface between the silicon islands so as to add to the growth of the islands. If at a particular temperature the migration distance of this precipitating silicon is less than half the distance between silicon islands, nucleation of non-single-crystalline silicon will occur on the oxide between the monocrystalline silicon islands. In an effort to avoid the formation of a non-single-crystalline silicon layer, and provide a deposition process which is not constrained by the geometry of the epitaxial nucleation site or sites or the growth time, the present invention was discovered.